In recent years much effort has been devoted toward producing absorbent materials for use in such body fluid absorbing products such as diapers, catamenial tampons and sanitary napkins. Heretofore, these products have employed naturally occuring cellulose fibers such as wood pulp, cotton and like. In U.S. Pat. No. 3,889,678 issued on June 17, 1975 to Chatterjee et al., a product is disclosed which comprises hydrophilic polymer moieties chemically grafted to the backbone of cellulose fibers. As is disclosed therein, the grafting of these polymer moieties have greatly enhanced the capacity of cellulose fiber systems to absorb and retain body fluids and these grafted materials have proven useful in a wide range of absorbent products. Similar disclosure is found in U.S. Pat. No. 4,105,033 issued on Aug. 8, 1978 to Chatterjee et al.
The above notwithstanding, it has been discovered that while the grafted fibers maintain the general appearance of the starting cellulosic material while providing enhanced absorptive properties, in one respect they behave adversely. Specifically, it has been discovered that grafted cellulose, when combined into pulp fluff exhibits a substantially greater bulk density than the starting cellulosic fibers. This unfortunate property manifests itself when the grafted fibers are produced in board form and subsequently comminuted in a mill or equivalent equipment. It is suspected that the fibers, being somewhat more brittle then wood pulp, for example, tend to crumble and dust to a degree. The resulting pulp fluff exhibits therefore a substantially lower void volume and has a harsher, more abrasive, feel. As a result, the use of the grafted cellulose fiber has been inhibited in certain diaper and sanitary protection products where low bulk density, high void volume and soft feel are desirable for user comfort and protection. Additionally, it has been discovered that the grafted cellulose materials, probably because of their brittleness, do not handle well when attempts are made to process these materials into an absorbent pad. Generally such processing involves an operation such as carding the fibers and when attempts are made to card these brittle fibers, they tend to dust, resulting in inefficient operation and waste. Still further, because these fibers are produced from naturally occurring cellulose fibers, their length is prescribed by nature. Accordingly it is not possible to tailor the length of the fibers to a desired value as is advantageous when attempting to blend these fibers with other fibrous materials. For example, blending is made easier by mixing fibers of comparable length and this optimum way of blending is constrained when employing grafted cellulose made from natural fibers.
For the above reasons, there is a need for a material which is capable of manifesting the high fluid capacity and retention characteristics of the grafted cellulose fibers described above without sacrificing the low bulk density and soft feel of fluffed wood pulp fibers.